Arteriole 479444 210726156 2008-05-07T03:19:34Z Marlith 4871029 fx [[Image:Illu capillary.jpg|thumb|300px]] An '''arteriole''' is a small diameter [[blood vessel]] that extends and branches out from an [[artery]] and leads to [[capillary|capillaries]]. <ref>{{cite book | last = Maton | first = Anthea | authorlink = | coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright | title = Human Biology and Health | publisher = Prentice Hall | date = 1993 | location = Englewood Cliffs, New Jersey | pages = | url = | doi = | id = | isbn = 0-13-981176-1}}</ref> Arterioles have thin [[muscle|muscular]] walls (usually only one to two layers of smooth muscle) and are the primary site of ''vascular resistance''<ref>[http://www3.umdnj.edu/histsweb/lab7/lab7arterioles.html arterioles<!-- Bot generated title -->]</ref>. [[Blood pressure]] in the arteries supplying the body is a result of the work needed to pump the [[cardiac output]] (the flow of blood pumped by the heart) through the ''vascular resistance'', usually termed [[total peripheral resistance]] by physicians and researchers. ==Natural fluctuation== The up and down fluctuation of the [[arterial]] blood pressure is due to the pulsatile nature of the [[cardiac output]] and determined by the interaction of the [[stroke volume]] versus the volume and elasticity of the major arteries. In a healthy vascular system the [[endothelium]], inner lining of arterioles and other blood vessels, is smooth and the vessel is relaxed. This healthy condition is promoted by the ample production of [[nitric oxide]] in the endothelium, which biochemical reaction is regulated by a complex balance of [[polyphenol]]s, various [[nitric oxide synthase]] [[enzyme]]s and L-[[arginine]]. In addition there is direct communication via gap junctions between the endothelial cells and the vascular smooth muscle ==Pathology== Any pathogen which constricts blood flow, such as [[stenosis]], will increase total peripheral resistance and lead to [[hypertension]]. ==Medication== The muscular contraction of arterioles is targeted by drugs that lower blood pressure ([[antihypertensive]]s), for example the [[dihydropyridine]]s ([[nifedipine]] and [[nicardipine]]), which block the [[calcium channel blocker|calcium conductance]] in the muscular layer of the arterioles, causing relaxation. This decreases the resistance to flow into peripheral vascular beds, lowering overall systemic pressure. ==Metarterioles== A "[[metarteriole]]" is an arteriole which bypasses capillary circulation.<ref>{{GeorgiaPhysiology|3/3ch9/s3ch9_2}}</ref> ==References== {{reflist}} {{cardiovascular_system}} [[Category:Cardiovascular system]] {{circulatory-stub}} [[bs:Arteriola]] [[de:Arteriole]] [[es:Arteriola]] [[fr:Artériole]] [[it:Arteriola]] [[lt:Arteriolė]] [[nl:Arteriole]] [[ja:細動脈]] [[nds:Arteriool]] [[pt:Arteríola]] [[ru:Артериола]]